Process of preparing pyridine and 3-picoline



PROCESS OF PREPARING PYRIDINE AND 3-PICOLINE Francis Cislak and William R. Wheeler,

Indianapolis, Ind.

N Drawing. Application February 12, 1954 Serial No. 410,044

6 Claims. (Cl. 260-290) Our present invention, which is a continuation in part of our co-pending application Serial No. 198,233, filed November 29, 1950, now abandoned, relates to a process of preparing pyridine and 3-picoline. More specifically, it relates to a process of preparing pyridine and 3-picoline by the interaction of acetylene, ammonia, and formaldehyde.

Pyridine is obtained commercially as a by-product of the coal-tar industry. The manufacture of coal-tar, coke, and related products starts with the placing of coal into a chamber and heating it out of contact with air. The coal is thereby decomposed into volatile products and into a non-volatile residue, coke. The volatile products, composed of condensable materials and non-condensable gases, are removed from the carbonization chamber and cooled, thereby condensing water and tar. After the complete removal of the water and tar, the remaining gas is passed through a preheater and then to a saturator. In the saturator the gas is contacted with dilute sulfuric acid. Ammonia and pyridine bases present in the gas are absorbed by the dilute sulfuric acid (about 6% H 80 The pyridine bases continue being absorbed until their concentration in the saturator bath Pyridine 115 .8 2-picoline 129.5 3 -picoline cut 143.6 Denaturing pyridine Up to 165 The 3-picoline cut is composed of about equal parts of 3-picoline (B.P. 143.9 C.), 4-picoline (B.P. 144.9 C.), and 2,6-lutidine (B.P. 143.7 C.). Because the boiling points of these three methylpyridines are so close together, it is not possible to separate them from each other by fractional distillation. The patent literature is replete with processes for isolating one or more of these compounds from the 3-picoline cut; all are complicated processes and with one exception are not commercially practicable.

The amount of pyridines that is normally obtainable as a by-product of coal carbonization is limited. At the present time, the amount is further curtailed because of economic considerations. The recovery of pyridine bases is incidental to the manufacture of ammonium sulfate. Unless there is a market. for the ammonium sulfate, it is unprofitable to recover pyridine bases from coke oven gases. Today, some of the largest producers of coal tar have discontinued recovering pyridine bases. The mar- 2,934,537 Patented Apr. 26, 1960 ket for ammonium sulfate has gradually shrunk, until now it is difficult to sell more than a small amount of that which is potentially available. With the steady increase in the use of anhydrous ammonia as a fertilizer, it is expected that the demand for ammonium sulfate will continue to decline.

For a number of years the demand for pyridines has exceeded the supply. If this demand is to be satisfied, it is imperative that a new source of pyridine be found. Many attempts have been made to synthesize pyridine bases. Some of the prior art describes processes for the synthesis of various alkylpyridines. Thus, British Patent 332,623, dated October 4, 1929, describes a process of catalytically condensing unsaturated hydrocarbons such as ethylene, butadiene, or in particular acetylene, or mixtures containing these substances, with ammonia (page 3, column 1, lines 19-23). By this process condensates are obtained which usually comprise two layers, the oily layer consisting mainly of heterocyclic bases which are difficultly soluble in water, such as collidines, lutidines, and quinolines, while the aqueous layer contains mainly water-soluble pyridine derivatives, in particular picoline, (page 3, column 2, lines 114-121).

British Patent 534,494, dated August 26, 1940, in discussing the process of the above mentioned British Patent 332,623 states that the process is not industrially useful as the yields of the bases obtained have been low and, large amounts of resins and other industrial by-products have been invariably formed. (page 2, column 1, lines 32-37.) Then the British Patent 534,- 494 goes on to describe a process for the manufacture of Z-methyl-S-ethylpyridine which consists in reacting in the liquid phase at temperatures between and 250 C. aliphatic aldehydes and ammonia or aliphatic amines Sufficient pressure must be used to maintain the reactants in the liquid phase at the temperature employed. (Page 2, column 1, lines 44-54).

US. Patent 1,882,518, dated October 11, 1932, describes a process of reacting acetylene with ammonia to prepare 2- and 4-methylpyridines as well as polymethylpyridines.

In spite of the years of research that have been devoted to the study of pyridine synthesis, no one has heretofore developed a commercial process for the simultaneous preparation of pyridine and 3-picoline.

We have found that we can react formaldehyde, acetylene, and ammonia to form pyridine and 3-picoline. Furthermore, we have found that we can so control the reaction that practically no Z-picoline or 4-picoline is formed. In other words, we can make 3-picoline which is uncontaminated by 4-picoline.

Our discovery is contrary to almost a century of prior art teaching. Formaldehyde and ammonia react to form hexamethylenetetramine in quantitative yield. This reaction which was first observed by Butlerov (1860) was later studied by Duden and Scharf, Eschweiler, and many other investigators. Its formation and structure are indicated in the equation shown below:

on, t

HEC CH methylene tetramine and obtain good yields of pyridine and 3-picoline.

The prior art teaches that acetylene reacts with ammonia to give mainly Z-picoline and 4-picoline.

We found that if we admix formaldehyde with the acetylene and ammonia, we suppress the formation of 4-picoline and cause the formation of pyridine and 3- picoline.

By our process we can prepare pyridine and 3-pico1ine economically and in commercial quantities with very good yields.

In carrying out our invention we mix the vapors of formaldehyde with acetylene and ammonia and pass the resultant mixture through a suitable reactor containing a catalyst. The temperature of the reactor is maintained preferably between about 400 C. and about 500 C. We prefer to carry out our process in a continuous manner although that is not necessary.

The reactor used may be of various types. We prefer the fluid catalyst type, similar to those normally used in carrying out cracking operations in the petroleum industry. Such reactors are of tubular form with suitable connections at entrance and exit. They are provided with means for supporting the fluid bed of catalyst, and are provided with any convenient means for heating them.

A highly satisfactory way of carrying out our invention is described more fully by means of the following specific examples:

Example 1 We prepared a gaseous mixture composed of about zinc fluoride, the catalyst was finely divided, and all of r picolines were recovered from the condensate by fractional distillation. The pyridine obtained amounted to about 0.25 pound for each pound of formaldehyde passed through the reactor.

Example 2 We prepared a gaseous mixture composed of one mole of acetylene, one mole of ammonia, and three moles of formaldehyde. We passed the mixture of vapors through a fluid catalyst type of reactor containing a fluidized catalytic bed of activated alumina (Alorco H-41) which had been impregnated with 10% zinc fluoride. The temperature of the reactor was maintained at about 425 C. The gaseous mixture of acetylene, ammonia, and formaldehyde was passed through at a superficial velocity of 1.25 feet per second. As this mixture of acetylene, ammonia, and formaldehyde passed through the reactor, a reaction occurred whereby pyridine and 3-picoline were produced. The vapors of the unchanged reactants and the reaction products were condensed as they emerged from the reactor, and the condensate was collected in a suitable receiver.

The condensate was composed fy pyridine compounds and non-basic or neutral compounds. In order to separate these two groups of compounds, the condensate was acidified to a pH of, 1 with sulfuric acid. The

pyridine base compounds present dissolved in the dilute sulfuric acid solution. The non-basic compounds were insoluble and formed a layer on top of the sulfuric acid solution. These were'separated by decantation. The last traces of non-basic compounds were removed by steaming the sulfuric acid solution. The sulfuric acid solution freed of non-basic contaminants was made strongly alkaline (pH 12.0) by the addition of sodium hydroxide. Pyridine bases separated from this strongly alkaline solution. They were removed by decantation. Any small amount of pyridines remaining in the alkaline solution were recovered by steam distillation and combined with the previously separated bases. After drying with flake caustic soda, the pyridine bases were fractionated to recover pyridine and 3-picoline. The pyridine recovered amounted to about 15%. The 3-picoline amounted to about 20%; as obtained from the fractionating column, the 3-picoline had a purity of more than 95%, clearly indicating that little if any 4-picoline was formed. 2-picoline was also recovered, but only in an amount of less than about 2% 7 Example 3 The process of Example 2 was repeated with the exception that the gaseous mixture passed through the reactor was composed of one mole of acetylene, one mole of ammonia, and one mole of formaldehyde. The pyridine bases recovered were subjected to fractional distillation. The pyridine recovered amounted to about 20%. The 3-picoline fraction amounted to about 18%; as obtained from the fractionating column, the 3-picoline had a purity of about indicating that 4-picoline was formed to some extent. 2-picoline was recovered in an amount of about 9% Example 4 The process of Example 2 was repeated with the exception that the gaseousmixture passed through the reactor was composed of one mole of acetylene and one mole of ammonia; no formaldehyde was used. The pyrdine bases obtained were subjected to fractional distillation. No pyridine was recovered. 2-picoline was recovered in an amount of 32.0%. 4-picoline was recovered in an amount of 28.0%; the 4-picoline had a purity of 93%, clearly indicating that little if any 3-picoline was formed.

Example 5 The process of Example 3 was repeated with the exception that the gaseous mixture passed through the reactor was composed of two moles acetylene, two moles ammonia, and one mole of formaldehyde. The pyridine bases recovered were subjected to fractional distillation. The pyridine recovered amounted to about 14%. The 3-picoline fraction amounted to about 17%; the 3-picoline as obtained from the fractionating column had a purity of about 50% indicating that as much 4-picoline was formed as there was of 3-picoline. The 2-picoline recovered amounted to about 16%.

Example 6 A zinc zeolite catalyst was prepared in the following manner. A four-inch diameter porcelain tube eight feet long was mounted vertically and filled with distilled water. Then 21.75 pounds of Decalso Permutit was slowly added to form an ion exchange bed approximately inches long.- A zinc chloride solution (3.5 pounds of zinc chloride and pounds of water) was flowed downward over the Permutit in order to replace zeolitic sodium by zinc ion. The zeolite'waswashed with 20 pounds of distilled water, drained, and placed in a drying oven. The zinc zeolite was dried for about 72 hours at 85 C. 7 It was then ground to 65 mesh and finer. (Decalso Permutit is a synthetic sodium-alumino-silicate used for water softening.)

,The process of Example 2 was repeated with the following exceptions. The zinc zeolite catalyst prepared above was used. The temperature of the reactor was maintained at 425 C. The gaseous mixture passed through the reactor was composed of two moles of acetylene, two moles of ammonia, and one mole of formaldehyde. The pyridine content of the water-free reaction product was about 29%. The 3 picoline fraction amounted to about 24%; as obtained from the fractionating column, the 3-picoline had a purity of about 50% indicating that 4-picoline was also formed.

Example 7 A gaseous mixture composed of one mole of acetylene, one mole of ammonia, and three moles of formaldehyde was passed through a suitable reactor containing a fluidized catalytic bed of activated alumina which had been impregnated with cadmium fluoride, the catalyst was finely divided, and all of it passed through 65 mesh. The reactor was maintained at a temperature of about 425 435 C. As the mixture of reactants passed through the reactor, a reaction occurred producing pyridine and 3-.picoline. The vapors of the unchanged reactants and the reaction products were condensed as they emerged from the reactor; the condensate was collected in a suitable receiver. The pyridine and the picolines were isolated from the condensate by fractional distillation. The pyridine content of the reaction product was about 20.9%. The 3-picoline amounted to about it was about 95% pure.

Example 8 The process of Example 7 was repeated with the exception that the catalyst used was a silica-magnesia catalyst impregnated with 10% zinc fluoride. The pyridine in the reaction product amounted to 19%. The yield of reaction product was about 0.50 to 0.60 pound per pound of acetylene passed through the reactor.

Example 9 A zinc Filtrol catalyst was prepared as follows:

2,500 grams of Filtrol 58 (which is a grade of montmorillonite clay having an amorphous or gel structure) was placed in a five-gallon glass container and a zinc chloride solution (227 grams of anhydrous zinc chloride was dissolved in 17 pounds of distilled water) was poured over the Filtrol. After this solution was poured over the Filtrol, a slurry was made by stirring for about one hour. The solids were removed from the slurry by filtration. The residue was removed from the filter and returned to the glass container. It was treated again with a zinc chloride solution prepared as mentioned above. The resulting slurry was filtered again. This process of slurrying the Filtrol and removing the aqueous solution was repeated fifteen times. Finally, the zinc Filtrol was thoroughly washed with distilled water. It was then dried in an oven and ground. Analyses on the thus-prepared catalyst showed it to contain about 2.5% zinc.

The process of Example 7 was repeated with the exception that the above prepared zinc Filtrol was used as catalyst. The condensate obtained was subjected to fractional distillation through an efiicient fractionating column to recover pyridine and 3-picoline. The pyridine recovered amounted to about 7.9%. The 3-picoline recovered amounted to about 11%; as recovered from the fractionating column, the purity of the 3-picoline was more than 95%.

Example 10 The process of Example 6 was repeated with the exception that the catalyst used was alumina impregnated with 10% cupric chloride. The pyridine content of the condensate was about 14.8%. The condensate amounted to about 0.35 to 0.40 pound per pound of acetylene used.

Example 11 Instead of using acetylene, we can use the hydrated form of acetylene, i.e. acetaldehyde. We prepared a gaseous mixture of one mole of acetaldehyde, one mole of ammonia, and two moles of formaldehyde. This mixture was reacted as was the mixture used in Example 2. The yields of pyridine, 3-picoline, and of 2-picolirie were as indicated in Example 2.

In place of the activated alumina, the silica magnesia, the Filtrol, and the zeolite as catalyst supports, we may use other catalyst supports, such as fullers earth, pumice, silica, and the like.

In place of the zinc fluoride, the cupric chloride, and the cadmium fluoride, we may utilize other catalysts, such as zinc chloride, cadmium chromate, cadmium molybdenate, lead chromate, zinc phosphate, and the like. As a matter of fact, we may cause acetylene, ammonia, and formaldehyde to react by passing the mixture of vapors over alumina itself. In other words, we may use the catalysts that have been found useful in the preparation of picolines from acetylene and ammonia.

As is evident from the specific examples given above, the proportions of the reactants may be varied widely. It is important, however, to have all three reactants present if pyridine is to be formed in any appreciable amount.

The temperature at which the reaction is conducted may be varied widely. In general, we prefer to have the reaction temperature above about 400 C. and below about 500 C. It has been our experience that at temperatures below about 400 C., we have too large a proportion of the reactants passing through without reacting. At temperatures above about 500 C., we find that our catalyst becomes inactivated more rapidly and we obtain too many side reactions.

We claim as our invention:

1. The process of preparing pyridine which comprises mixing the vapors of acetylene, ammonia, and formaldehyde, passing the resultant mixture through a reactor containing a catalyst comprising an activated alumina impregnated with Zinc fluoride maintained at a temperature between about 400 C. and about 500 C. and recovering pyridine from the reaction product.

2. The process of preparing pyridine which comprises mixing the vapors of acetylene, ammonia, and formaldehyde, passing the resultant mixture through a reactor containing a catalyst comprising activated alumina impregnated with 10% zinc fluoride maintained at a temperature between about 400 C. and about 500 C. and recovering pyridine from the reaction product.

3. The process of preparing pyridine which comprises mixing the vapors of acetylene, ammonia, and formaldehyde, passing the resultant mixture through a reactor containing a catalyst comprising activated alumina impregnated with 10% zinc fluoride maintained at a temperature between about 470 C. and 480 C., and recovering pyridine from the reaction product.

4. The process of preparing pyridine which comprises mixing the vapors of acetylene, ammonia, and formaldehyde, passing the resultant mixture through a reactor containing a catalyst comprising activated alumina impregnated with 10% zinc fluoride maintained at a temperature between about 415 C. and 425 C., and recovering pyridine from the reaction product.

5. The process of preparing pyridine which comprises preparing a gaseous mixture composed of about two parts of acetylene, of about four and one-half parts of ammonia, and of about one part of formaldehyde, passing the resultant mixture through a reactor containing a catalyst comprising activated alumina impregnated with 10% zinc fluoride maintained at a temperature between about 470 C. and 480 C., and recovering pyridine from the reaction product.

6. The process of preparing pyridine which comprises preparing a gaseous mixture composed of about two parts of acetylene, of about four and one-half parts of ammonia, and of about one part of formaldehyde, passing 7 the resultant rlnixturecthrough a reactor containing a i FOREIGN PATENTS catalyst comprlsmg actlvated alumma impregnated wlth 525,652 V'G "In"- June 9, 1931 10% Zinc fluoride maintained at a temperature between abbut'415 C. and 425 C. and recovering pyridine from 3 Great Brltam July 1930 the reaction product. 5 534,494 Great Britain Mar. 7, 1941 References Cited in the file of this patent I O ER REFERENCES 0 UNITED STATES PATENTS Ser. No. 387,106, Stitz (A.P.C.), published July 13, 1,882,518 Nicodemus Oct. 11, 1932 1943' 2,700,042 Aries Jan. 18, 1955 

1. THE PROCESS OF PREPARING PYRIDINE WHICH COMPRISES MIXING THE VAPORS OF ACETYLENE, AMMONIA, AND FORMALDEHYDE, PASSING THE RESULTANT MIXTURE THROUGH A REACTOR CONTAINING A CATALYST COMPRISING AN ACTIVATED ALUMINA IMPREGNATED WITH ZINC FLUORIDE MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 400*C. AND ABOUT 500*C. AND RECOVERING PYRIDINE FROM THE REACTION PRODUCT. 